1. Field of the Invention
This invention relates to protecting an elongate substrate, and more particularly to a method of protecting an elongate substrate with a flat sheet wrapped therearound and held together by a novel flat sheet closure device.
2. Discussion of the Prior Art
Wraparound sleeves are widely used as protective closures in the pipe, electrical power distribution, and telecommunication industries for environmentally sealing, electrically insulating and/or strengthening the pipe, conduit, or cable. Numerous wraparound sleeve closures and methods are known in the art. One class of closures is a flat sheet which has been overlappingly wrapped with no additional parts being required to effect the closure. Unwrapping is prevented by such means as, for example, adhesive bonding, internal forces causing the edges to cooperatively curl together, and/or internal forces reinforcing the wraparound, such as a high degree of friction from multiple turns upon wrapping. The strength and effectiveness of such closures is often marginal and such closures can be difficult to install under typical conditions of use.
A second class of flat sheet closures consists of those having additional closure parts. These additional parts may be either, for example, a self-adhesive patch, a clamp that holds the two sheet ends separately, or a clamp system that holds the two sheet ends in overlapping frictional contact, such as, a buckle system. Clamp configurations which hold the two sheet ends separately often have barbs, teeth or other such projections which can perforate the sheet and may induce tearing thereof. This is a problem for polymeric sheets and especially for elastomeric sheets. Dimensionally-recoverable sheets generate large forces on recovery tending to cause the separation of the sheet ends joined by these clamps. Separation of parts and tearing pose difficult design problems generally unsolved by the prior art. These problems are compounded by other factors, such as, the lack of protection of the elongate substrate under the clamp and the possibility of air being trapped under the clamp thereby creating a channel leak path through which water may penetrate and corrode or electrically short-out the substrate to be protected or insulated.
An example of a clamp system that holds the two sheet ends in overlapping frictional contact is given in U.S. Pat. No. 4,083,087 to C. Clark Hale, herein incorporated by reference. Hale discloses two pins around which the opposing ends of a flat band are wrapped in opposing directions and which are locked into place by means of an elongate channel clipped or slid thereover. A basic omega closure is taught in U.S. Pat. No. 4,219,051 to A. H. L. D'Haeyer, herein incorporated by reference, in which two sheets are overlapped around a rod in opposing directions and are clamped between the rod and a C-shaped channel. Such closures are prone to slippage of the lapped sheet, especially if the sheet is a dimensionally-recoverable sheet, most especially if the sheet is a heat-shrinkable sheet.
A third class of sheet closures consists of those having profiles. Profiles may be continuous or discontinuous. Continuous profiles, such as a grooved sheet edge, are typically extruded with the sheet. Discontinuous profiles, such as cut interlocking sheet edge shapes, are typically machined such as by cutting. Profiled sheets are hence more expensive to manufacture and must be inventoried and sold in sizes, but do offer improved strength, especially if combined with additional parts.
U.S. Pat. No. 3,455,366 to R. H. Ellis, herein incorporated by reference, is one example of a "rail and channel" closure, i.e. a sheet having abuttable opposing edges, each edge having an elongate ridge profile, collectively forming a rail when the sheet is wrapped around a pipe to abut the edges, which rail may be fastened by slipping a flexible channel thereover. Although a strong closure is obtained, installation of the channel can be difficult for closures of long length because of the frictional drag of a long length of channel.
European Patent Publication No. 23,418 to A. C. Egerton Limited, herein incorporated by reference, discloses in part a "rail and channel" type closure having a pair of channels, which clip together, each channel fitting over a profiled edge. The channels in such a design can be preassembled at the manufacturing facility and hence the installation difficulty of running a long channel in the field is largely eliminated. The sheets must be manufactured, inventoried and sold in sizes determined by the rail position. Disclosed also by Egerton is a flat sheet closure which clips together and features tabs folded down from a pair of perforated strips, which tabs pierce the sheet near its opposing edges to grip it. One such strip is placed along each of the pair of opposing sheet ends, the strip terminating along its long edge in a mateable clipping arrangement. Piercing or perforating polymeric sheets may be acceptable for some applications, but when elastomeric sheets or dimensionally-recoverable sheets, especially heat-shrinkable sheets are used tearing can result.